fix(dialogs-style): Remove box shadow from header and footer

css/_atlaskit_overrides.scss

  * Override @atlaskit/modal-dialog header styling
  */
 .atlaskit-portal [role="dialog"] header {
+    box-shadow: none;
     .jitsi-icon {
         cursor: pointer;
     }
     }
 }
 
+/**
+ * Override @atlaskit/modal-dialog footer styling.
+ */
+ .atlaskit-portal [role="dialog"] footer {
+     box-shadow: none;
+ }
+
 /**
  * Make header close button more easily tappable on mobile.
  */